1. Field of the Invention
The present invention relates to optical recording disks, and more particularly to an optical recording disk well suited for erasable magnetooptical recording.
2. Description of the Prior Art
In a magnetooptic disk, a layer of ultraviolet-cured resin (hereinafter, called "UV-cured resin") is successively overlaid with a film of SiO or the like for enhancing the Kerr rotation angle, a recording film of TbFeCo system or the like, and a protective layer of SiO or the like. These films are formed by thermal evaporation or sputtering. Heretofore, such films have been, for example, ones described in `Photographic Science and Engineering` 28, No. 3, 1984, p. 128.
In a case where, of the film forming methods, especially sputtering is employed for providing the enhancement film etc., microscopic wrinkles appear on the surface of the UV-cured resin layer. The wrinkles recur at periods of several--ten .mu.m. They increase noise to drastically degrade the carrier-to-noise ratio (C/N ratio).
It has been found that the situation of appearance of the wrinkles differs depending upon the kind of the UV-cured resin material which forms a subbing layer. As a cause for the appearance of the wrinkles, the thermal property of the UV-cured resin material is pertinent. More specifically, the temperature of a substrate rises during the sputtering process, i.e., to about 100.degree. C. The thin films of the inorganic materials having high stresses are stacked on the surface of the UV-cured resin layer which is in such a high temperature state. Accordingly, the UV-curable resin whose heat resistance is low is distorted to undergo wrinkles by the stresses.